[time-nuts] HP 5065A rubidium lifetime
Bob Camp
lists at rtty.us
Sun Mar 21 02:15:35 UTC 2010
Hi
You make a tightly twisted pair. The ides is to get the magnetic field to cancel out.
Bob
On Mar 20, 2010, at 9:14 PM, J. L. Trantham wrote:
> Do you make a 'twisted pair' and then wind that or just wind two parallel
> wires around the cylinder?
>
> Joe
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Bob Camp
> Sent: Saturday, March 20, 2010 7:59 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] HP 5065A rubidium lifetime
>
>
> Hi
>
> I think I can answer part of that, though I've never dissected a 5065.
>
> To make the heater work right you need the proper resistance / foot heater
> wire. Cupron is a pretty typical material if you want to solder to it.
> Nicrome is fine if you are welding to it. THe real trick here is to find
> somebody with a spool of the right stuff and then beg a few feet from them.
>
> Doing a hairpin and then twisting is much harder to do right than winding it
> tightly and then shorting the end of the pair.
>
> The easy way to make the twisted pair is to use an electric drill. Once you
> wind the stuff, both ends are scrap, but the part in the middle is quite
> good. You loose an inch on each end and get a few feet (or how ever much)
> out of the middle.
>
> Since the maximum temperature the oven can go over ambient rises as the
> heater resistance goes down (good old P = E^2/R) you might put a heater on
> thats a slight bit higher in resistance than the original. that would be a
> problem when it gets to 0 (or -20) in you basement, but it would take the
> load off of the rest of the parts.
>
> Bob
>
>
> On Mar 20, 2010, at 8:30 PM, J. L. Trantham wrote:
>
>> Chuck,
>>
>> Can you provide any other information about this repair?
>>
>> How much disassembly of the RVFR, what kind of prep of the lamp
>> casing, how much wire, where did you find the wire, did you 'bend' the
>> wire into a 'hairpin' or did you wind two wires then short one end and
>> feed the power from the other end, what kind of prep for the outside
>> cylinder, what kind of 'jig' to hold everything in place while
>> applying the urethane foam, etc., etc.
>>
>> I have two of these and one arrived dead after which I 'killed' it
>> some more with a total melt down. If this should arise again, a
>> repair guide might be very helpful.
>>
>> Joe
>>
>> -----Original Message-----
>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]
>> On Behalf Of Chuck Harris
>> Sent: Saturday, March 20, 2010 7:35 AM
>> To: Discussion of precise time and frequency measurement
>> Subject: Re: [time-nuts] HP 5065A rubidium lifetime
>>
>>
>> I can't say for certain.
>>
>> The heating element is a single layer of formvar coated nichrome
>> wire.... about #36 gage. To avoid magnetic fields, they wound it
>> bifilar, and shorted the far end of the bifilar wires... forming a
>> "hairpin" loop.
>>
>> I found a short about 1 inch into the 5 inch winding, and the oven
>> driver transistor was open circuited. The 1 inch that wasn't shorted
>> was surrounding the area of the lamp assembly.
>>
>> I recall that the oven fuse was ok.
>>
>> -Chuck Harris
>>
>> John Miles wrote:
>>> What was the root cause of the oven failure in your case?
>>>
>>> -- john, KE5FX
>>>
>>>> -----Original Message-----
>>>> From: time-nuts-bounces at febo.com
>>>> [mailto:time-nuts-bounces at febo.com]On
>>>> Behalf Of Chuck Harris
>>>> Sent: Friday, March 19, 2010 9:58 PM
>>>> To: Discussion of precise time and frequency measurement
>>>> Subject: Re: [time-nuts] HP 5065A rubidium lifetime
>>>>
>>>>
>>>> When my 5065A had its oven failure, it got so hot that it melted all
>>>> of the solder joints on the lamp board. I resoldered the joints,
>>>> rewound the oven
>>>> winding, and foamed the unit with some spray can urethane (Great
>>>> Stuff), and
>>>> had it working again for a couple of years. Then something else failed.
>>>>
>>>> I'd sure like to fix it, but Scott McGrath, representing himself as
>>>> an employee of Harvard University, borrowed my manual more than a
>>>> year ago, and refuses to return it. Oh well!
>>>>
>>>> -Chuck Harris
>>
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>
>
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